NO20130204A1 - Turbine stage with wavy surface and flush channel - Google Patents

Abstract

A turbine stage includes a series of airfoils joined by corresponding platforms to define flow passages therebetween. Each airfoil includes opposite pressure and suction sides and extends in chord between opposite front and rear edges. Each platform has a corrugated flow surface including a flushing trough which begins tangentially in a mixing region of the platform. The flushing trowel extends axially to the suction side of the airfoil, the actuator of the leading edge, to channel a flushing flow.

Description

BACKGROUND

[0001] The present disclosure generally relates to gas turbine engines, and turbomachinery, and more specifically turbines therein.

[0002] In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustion chamber to generate hot combustion gases. Turbine stages extract energy from the combustion gases to drive the compressor, while also driving an upstream fan in a turbofan aircraft engine application, or driving an external drive shaft for marine and industrial applications.

[0003] A high pressure turbine (HPT) immediately follows the combustor and includes a stationary turbine nozzle which discharges combustion gases into a row of rotating first stage turbine rotor blades extending radially outward from a supporting rotor disc. The HPT may include one or more stages or rotor blades and corresponding turbine nozzles.

[0004] After the HTP there is a low pressure turbine (LPT) which typically includes several stages of rotor blades and corresponding turbine nozzles.

[0005] Each turbine nozzle includes a row of stator vanes with radially outer and inner end walls in the form of arcuate rings which carry the vanes. The turbine rotor blades include corresponding airfoils fully joined with radially inner end walls or platforms, which in turn are supported by corresponding dovetails which provide for mounting of the individual blades in dovetail grooves formed in the perimeter of the supporting rotor disc. An annular shroud surrounds the radially outer tips of the rotor airfoils in each turbine stage.

[0006] The stator vanes and rotor blades have corresponding airfoils which include generally concave pressure sides and generally convex suction sides extending axially in chord between opposite leading and trailing edges. Adjacent vanes and adjacent blades form corresponding flow passages therebetween, bounded by the radially inner and outer end walls.

[0007] During operation, combustion gases are released from the combustion chamber and flow axially downstream as a core flow through the respective flow passages defined between the stator vanes and the rotor blades. In addition, flushing air from a flushing cavity located upstream of the front edge of the airfoil is emitted as a flushing flow that prevents intake of hot core flow below the main gas flow, and possibly provides a cooling effect on the platform and airfoils. The aerodynamic contours of the vanes and blades, and corresponding flow passages between them, are precisely configured to maximize energy extraction from the combustion gases, which in turn rotate the rotor from which the blades extend.

[0008] The complex three-dimensional (3D) configuration of the vane and blade airfoils is tailored to maximize efficiency during operation, and varies radially in span along the airfoils, as well as axially along the chords of the airfoils between the leading and trailing edges. The velocity and pressure distributions of the combustion gases and the purge air over the airfoil surfaces, as well as inside the corresponding flow passages, also consequently vary.

[0009] Unwanted pressure losses in the flow path of the combustion gas therefore correspond to a desired reduction in the turbine's aerodynamics and the turbine's overall efficiency. For example, the combustion gases enter the corresponding rows of vanes and blades in the flow passages between them, and are necessarily split at the respective front edges of the airfoils. In addition, mixing of the purge air flow and core flow can lead to inefficiency of the turbine.

[0010] The localization of stagnation points for the incoming combustion gases extends along the leading edge of each airfoil, and corresponding boundary layers are formed along the pressure and suction sides of each airfoil, as well as along each radially outer and inner end wall that jointly delimits the four sides of each flow passage. In the boundary layers, the local velocity of the combustion gases varies from zero along the end walls and airfoil surfaces to the non-retained velocity of the combustion gases where the boundary layers terminate.

[0011] Turbine losses can occur from a variety of sources, such as secondary flows, shock-loss mechanisms, and mixing losses. One common source of turbine pressure loss is the formation of horseshoe vortices generated when the combustion gases split in their motion around the leading edges of the airfoil. A total pressure gradient is affected in the boundary layer flow at the junction between the leading edge and the end walls of the airfoil. The pressure gradient at the leading edges of the airfoils forms pairs of counter-rotating horseshoe vortices that move downstream on the opposite sides of each airfoil near the end wall. The two vortices travel aft along the opposite pressure and suction sides of each airfoil, and behave differently due to the different pressure and velocity distributions along these. For example, computational analysis shows that the suction-side vortex migrates away from the end wall towards the trailing edge of the airfoil, and then interacts, following the trailing edge of the airfoil, with the pressure-side vortex flowing aft thereto.

[0012] The interaction between the pressure and suction side vortices occurs near the mid-span region of the airfoils and forms a total pressure loss and a corresponding reduction in the efficiency of the turbine. These vortices also form turbulence and increase unwanted heating of the end walls.

[0013] Since the horseshoe vortices are formed at the joints between the turbine rotor blades and their integral foot platforms, as well as at the joints between the nozzle stator vanes and their outer and inner rings, the corresponding loss in turbine efficiency is formed, as well as additional heating of the corresponding end wall components.

[0014] Likewise, pressure gradients for the cross-passage between the pressure and suction sides of the blade cause secondary flow structures and vortices that change the desired aerodynamics of the blade, causing loss in turbine efficiency as well as possible heating of the end walls and even the blade.

[0015] At the leading edges of the turbine blades, and more specifically at a joint between the leading edge and the leading edge flush cavity, secondary flow structures and mixing of a flush flow from the leading edge flush cavity result in mixing loss. In addition, the secondary flow structures result in mixing of the flush flow with the main core flow, resulting in a trajectory for the flush flow that is distant from the platform. These secondary flow structures result in high heat concentrations in the area where the turbine blade meets the blade endwall structure.

[0016] Accordingly, it is desirable to provide an improved turbine stage to reduce horseshoe vortex effects and secondary flow effects, as well as increase aerodynamic load while controlling heat distribution and efficiency or improve efficiency and thermal load while maintaining aerodynamic load and/ or production of torque.

SHORT DESCRIPTION

[0017] In accordance with an exemplary embodiment, a turbine stage with a wave-shaped surface with a flushing trough is disclosed. The turbine stage comprises a row of airfoils fully joined with corresponding platforms and spaced laterally to define respective flow passages therebetween for channeling gases. Each flow passage has a width. Each of said airfoils includes a concave pressure side and a laterally opposite convex suction side which extends in line between opposite front and rear edges. At least some of the platforms have an undulating flow surface that includes a flush trough extending tangentially into a mixing region and at least a portion of a flush cavity wall of the platform, and extending axially toward the suction side of the airfoil, aft of the leading edge, to channel a flush current.

[0018] In accordance with another exemplary embodiment, a turbine stage with a wave-shaped surface with a flushing trough is disclosed. The turbine stage comprises a row of airfoils fully joined with corresponding platforms and spaced laterally to define respective flow passages therebetween for channeling gases. Each of the flow passages has a defined width. Each of said airfoils includes a concave pressure side and a laterally opposite convex suction side which extends in line between opposite front and rear edges. At least some of said platforms have an undulating flow surface including a flush trough extending tangentially into a mixing area and at least a portion of the flush cavity wall of the platform, a bulge abutting said pressure side aft of said leading edge, and a bowl bordering up to said flush trough and said suction side aft of said front edge of said respective airfoils. The flushing trough extends axially towards the suction side of the airfoil to gradually transition into the bowl and channel a flushing flow.

[0019] In accordance with yet another exemplary embodiment, a turbine stage with a wave-shaped surface with a flushing trough is disclosed. The turbine stage comprises a turbine blade. The turbine blade comprises an airfoil completely joined to a platform, and has laterally opposite pressure and suction sides which extend parallel between axially opposite leading and trailing edges. The platform includes a flush trough extending tangentially into a mixing area and at least a portion of a flush cavity wall of the platform. The wash trough extends axially towards the suction side of the airfoil, aft of the leading edge, to channel a wash flow.

[0020] Other purposes and advantages of the present disclosure will become clear upon reading the following detailed description and the appended claims with reference to the accompanying drawings. These and other features and improvements in the present application will be clear to someone with ordinary technical knowledge in the field of technology when reviewing the following detailed description when viewed together with several drawings and the attached claims.

DRAWINGS

[0021] The above and other features, aspects and advantages of the present disclosure will be better understood when the following detailed description is read with reference to the accompanying drawings, where like characters represent like parts throughout the drawings, where:

[0022] Figure 1 is a front-aft side view of exemplary turbine blades in a turbine stage row according to one embodiment;

[0023] Figure 2 is a planar sectional view through the leaves illustrated in fig. 1 and taken along line 2-2 in fig. 1 according to an embodiment;

[0024] Figure 3 is an isometric view of the suction side of the blades illustrated in fig. 1 according to an embodiment;

[0025] Figure 4 is an isometric view of the print side of the blades illustrated in fig. 1 according to an embodiment;

[0026] Figure 5 is an isometric view facing aft-front of the blades illustrated in fig. 1 according to an embodiment;

[0027] Figure 6 is a front-aft side view of exemplary turbine blades in a turbine stage row according to another embodiment; and

[0028] Figure 7 is a planar sectional view through the leaves illustrated in fig. 6 and taken along line 7-7 in fig. 6 according to an embodiment.

DETAILED DESCRIPTION

[0029] With reference to the drawings, where identical reference numerals denote the same elements throughout the different views, it is illustrated in fig. 1 two exemplifying first-stage turbine rotor blades 10 which in the circumferential direction adjoin each other in a full row thereof in a corresponding turbine stage in a gas turbine engine. As indicated above, combustion gases 12 are formed in a conventional combustion chamber (not shown) and discharged in an axial downstream direction through the row of turbine blades 10 as a core stream 13. The turbine blades 10 extract energy from the combustion gases 12 to drive a supporting rotor disk (not shown) which the blades 10 are mounted on.

[0030] The turbine stage includes a complete row of blades 10, each blade 10 having a corresponding airfoil 14 fully joined to a corresponding radially inner end wall or platform 16 at a foot end. Each platform 16 is in turn fully joined to a corresponding axial entry dovetail 18, conventionally configured to carry the corresponding turbine blade 10 in the perimeter of the rotor disk.

[0031] Each airfoil 14 includes a generally concave pressure side 20 and a circumferentially or laterally opposite, generally convex suction side 22 which extends axially in line between opposite front and rear edges 24, respectively 26. The two edges 24, 26 extend radially in span from the foot to the tip of the airfoil 14.

[0032] As shown in fig. 1 and 2, each airfoil 14 may be hollow and include an internal cooling circuit 28 bounded by the opposite pressure and suction sides 20, 22. The cooling circuit 28 may have any conventional configuration and include inlet channels extending through the platform 16 and the dovetail 18 for receiving cooling air 30 drained from the compressor in the engine (not shown).

[0033] The cooling air 30 is typically released from each airfoil 14 through several rows of film cooling holes 32 located where desired on the pressure and suction sides 20, 22 of the airfoil 14, and which are typically concentrated near the front edge 24 thereof. Each airfoil 14 also typically includes a row of cooling holes 34 at the rear edge, which emerge through the pressure side 20 of the airfoil 14 just before the thin rear edge 26 thereof.

[0034] The exemplary turbine blades 10 illustrated in fig. 1 and 2 may have any conventional configuration of the airfoil 14, the platform 16 and the dovetail 18 to extract energy from the combustion gases 12 during operation. As indicated above, the platform 16 is fully joined at the foot end of the airfoil 14, and determines the radially internal flow boundary for the combustion gases 12, or core flow 13.

[0035] The blades 10 are mounted in a row around the perimeter of the rotor disk, with adjacent airfoils 14 spaced in the circumferential or lateral direction to define flow passages 36 therebetween with a passage width "x" defined between adjacent leading edges 24 (as best illustrated in Fig. 2) for channeling the combustion gases 12 and a purge flow 15 of purge air from a purge air cavity (not shown) axially in the downstream direction during operation.

[0036] Each inter-airfoil flow passage 36 in the turbine stage illustrated in FIG. 1 and 2 are therefore determined and delimited by the pressure side 20 of one airfoil 14, the suction side 22 of the next nearby airfoil 14, the corresponding pressure and suction side parts 20, 22 of the nearby platforms 16, and the radially outer turbine casing (not shown) which surrounds the radially outer tips of the airfoils 14 in the complete row of turbine blades 10.

[0037] As indicated above in the background chapter, the combustion gases 12 flow through the corresponding flow passages 36 as core flow but 13 during operation, and are necessarily split by the individual airfoils 14. The high velocity combustion gases are split in the circumferential direction at the corresponding front airfoil edges 24 with a stagnation pressure that is there, and with the formation of corresponding boundary layers along the opposite pressure and suction sides 20, 22 of the airfoil 14. Furthermore, the combustion gases 12 also form a boundary layer along the individual blade platforms 16 when the gases split around the front edge 24 of the airfoil at its joining with platform 16.

[0038] In addition, the air flow from the scavenge flow cavity located upstream of the airfoils 14 flows through the corresponding flow passages 36 as the scavenge stream 15. Minimizing an ejection of the scavenge stream 15 as a percentage of core flow but 13 leads to an increase in the static pressure downstream of the airfoil 14. This effect helps to move the shock at the trailing edge 26 upstream, which reduces the loss at the trailing edge in the airfoils 14.

[0039] The split core flow 13 along the blade platforms 16 results in a pair of counter-rotating horseshoe vortices that flow axially downstream through the flow passages 36 along the opposite pressure and suction sides 20, 22 of each airfoil 14. These horseshoe vortices form turbulence in the boundary layers , and migrates radially outward towards the midspan regions of the airfoils 14 and produces a loss in total pressure and reduces the turbine's efficiency. The horseshoe vortices are energized by the presence of the flushing cavity and the flushing flow 15 which modifies the static pressure gradient for the cross passage.

[0040] The exemplary turbine engine stage illustrated in FIG. 1 may be of any conventional configuration, such as specifically designed as a first stage HPT rotor for extracting energy from the combustion gases 18 to drive the compressor in a typical manner. As illustrated, the incoming combustion gases 12 are split along the leading edges 24 of the airfoils to flow axially through the corresponding flow passages 36 as the core stream 13 in the downstream direction, while the incoming scavenge air flows over a shoulder area, or mixing area, 40 of the platforms 16, where the mixing area 40 is determined as the radius between a flushing cavity wall 41 and the platform 16 surface. The purge air flows and mixes with the core stream 13 to flow axially through the corresponding flow passages 36 as the purge stream 15 in the downstream direction.

[0041] The concave profile of the pressure sides 20 and the convex profile of the suction sides 22 are specifically configured to effect different velocity and pressure distributions for maximizing the extraction of energy from the combustion gases 12. The platforms 16 define radially inner end walls that bound the combustion gases 12, the gases also bounded radially outwards by the surrounding turbine casing (not shown).

[0042] In the illustrated configuration, the incoming combustion gases 12 at the junction between the platforms 16 and the leading edges 24 are exposed to the horseshoe vortices, fired below by modification of the static pressure gradient of the cross-passage for the scavenge flow 15. The combustion gases 12 advance through the flow passages 36 along the opposite pressure 20 and suction sides 22 of the airfoils 14. As indicated above, these vortices create turbulence, reduce the aerodynamic efficiency of the turbine stage, and increase the heat transfer heating of the platforms 16.

[0043] The platforms 16 initially illustrated in FIG. 1 is therefore specifically configured with wavy or contoured flow surfaces that minimize mixing of the purge stream 15 with the core stream 13 to minimize losses and confine the combustion gases 12 to reduce the strength of the horseshoe vortices. A first exemplary configuration of the wave-shaped platforms 16 is shown generally in FIG. 1 with isoclines for common elevation from a nominally axisymmetric platform. Figure 2 illustrates in more detail the isoclines in fig. 1 in planar view. A second exemplary configuration of the corrugated platforms 16 is shown generally in FIG. 6 and fig. 7, and illustrates isoclines for common elevation from a nominally axisymmetric platform, respectively a more detailed illustration of the isoclines in planar view.

[0044] With more specific reference to fig. 1 and 2, modern computational fluid dynamics has been used to study and determine the specific 3D contours of the platforms 16 for weakening the horseshoe vortices and minimizing mixing of the wash flow 15 with the core flow 13 and intake into the wash cavity, while correspondingly improving the turbine's aerodynamic efficiency. The wave-shaped platforms 16 illustrated in fig. 1 and 2 includes a wave or wash trough 38 configured to extend into the mixing area 40 and at least a portion of a wash cavity wall 41 of the platform 16, with a lower elevation (-) relative to a nominal axisymmetric platform surface of a conventional platform that delimits zero reference (the surface and forms a depression or trough therein which modifies the mixing area 40 and at least a portion of the wall cavity 41. In the illustrated embodiment, the flushing trough 38 is formed tangentially in the mixing area 40 and extends into the flush wall cavity 41 with a location of maximum depth approximately the midway width "x" of the passage 36, between the front edges 24 of adjacent airfoils 14, may extend in a lateral direction approximately 60% of the width "x" of the passage 38. In a alternative embodiment, the flushing trough 38 can be formed tangentially in the mixing area 40 and extend into at least a part of the flushing wall cavity 41 and have a local measurement of maximum depth anywhere between -10% to 60% of the width "x" of the passage 36 between the front edges 24 of adjacent airfoils 14, where such measurements are measured starting from the front edge 24 of a first airfoil 14 towards the suction side 22 of the first airfoil 14, and extends towards the front edge 24 of a second nearby airfoil 14 at the pressure side 20. In one embodiment, the flushing trough 38 can extend in a lateral direction approximately 60% of the width "x" of the passage 38. In yet in another embodiment, the flush trough 38 may be formed substantially tangentially in the mixing area 40 and extend into at least a portion of the flush wall cavity 41 and have a maximum depth location anywhere between -10% to 60% of the width "x" of the passage 36 between the leading edges 24 of adjacent airfoils 14, as previously described, and located in a position axially downstream of the leading edges 24 and within the passage 36 formed therebetween.

[0045] The flush trough 38 is configured to modify the mixing area 40 and at least a portion of the flush cavity wall 41 of the airfoil 14 to facilitate the flush flow 15 into the core flow 13. More specifically, the flush trough 38 is configured to maintain a trajectory for the flush flow 15 closer to the platform 16 on the suction side 22 to minimize a subsequent downward sweep of the hot core flow 13 on the pressure side 20 of the airfoil 14 to fill back with fluid. The flushing trough 38 and the flushing stream 15 serve to modify the static pressure gradient of the cross passage which supplies energy to the horseshoe vortices.

[0046] In addition, the presence of the scavenge trough 38 allows manipulation of the operational thermal profile at the leading edge 24 of the airfoil 14. This is because the modification in the scavenge flow 15 can be altered or cause a reduction in convective mixing and/or heat transfer which would normally bring core - the stream 13 in contact with the end walls. This aspect of the present disclosure allows manipulation of the thermal profile via the reduction in mixing of the purge stream 15 with the core stream 13. Consequently, a desired thermal distribution can be achieved and it can be optimized, resulting in a reduction in the required cooling.

[0047] In one embodiment, an optional local bulge or bulge 46 may be included in addition to the flush trough 38, rising upward (+) into the flow passage 36 relative to the nominal axisymmetric reference surface fl In addition, in yet another embodiment, a integral recess or bowl 48 be included in addition to the flush trough 38 which has a lower elevation (-) in relation to the nominal axisymmetric platform surface fl to form a recess therein. In yet another embodiment, a bulge 46 and a bowl 48 may be included in addition to the flushing trough 38.

[0048] It is taken ad notam that the specific sizes and distances for the airfoils 14 are chosen for a specific engine design and mass flow rate through it. The arched sidewalls of the airfoils 14 typically define a flow passage 36 in the circumferential direction therebetween, which converges in an axial downstream direction from the leading edges 24 to the trailing edges 26.

[0049] The trailing edge 26 of one airfoil 14 typically forms a constriction with a minimum flow area along its perpendicular intersection near the center chord of the suction side 22 of a nearby airfoil 14. The flow area in the flow passage 36, including the minimum flow area in the constriction thereof, is preselected for a given engine application, and is therefore controlled both by the radially inner end wall bounded by the platform 16, as well as the radially outer end walls bounded by the turbine shroud (not illustrated).

[0050] The reference platform surface can therefore be conventionally determined as the conventional axisymmetric surface determined by circular arcs around the circumference of the turbine stage, and can be used as the zero reference elevation illustrated in fig. 2. In an embodiment that includes a flush trough 38, a bulge 46 and a bowl 48, the bulge 46 rises outward in elevation (+) from the zero reference plane or surface, while the flush trough 38 and bowl 48 extend in depth (-) below the reference plane or surface. In this way, the trough 38, the bulge 46 and the bowl 48 can complement and offset each other to maintain the desired or given flow area for each flow passage 36.

[0051] The flushing troughs 38, the bulges 46 and the bowls 48 illustrated in fig. 1 and 2 are preferably located specifically to reduce the strength of the horseshoe vortices, which minimizes losses due to secondary flows, minimizes mixing of the flush flow 15 from a flush cavity at the leading edge with the main core flow 13, minimizes the intake of the hot core flow into in the scavenge cavity, modifying the static pressure gradient of the cross-passage that supplies energy to the horseshoe vortices, all of which improves the turbine's aerodynamic efficiency. In the illustrated embodiment, the flush trough 38 is configured at a position near the leading edge 24 of the suction side 22, and is formed to extend into the shoulder, or mixing area 40, of the platform 16. The bulge 46 is configured to directly abut the airfoil pressure side 20 at a position downstream, or aft of, the leading edge 24. The bowl 48 is configured to directly border the flush trough 38 and the airfoil suction side 22 aft of the leading edge 24.

[0052] By using the flushing trough 38, the flushing flow 15 enters the core flow 13 more easily, with the trajectory of the flushing flow 15 maintained closer to the platform 16 as it is lifted by the platform 16 on the suction side 22. This minimizes a subsequent sweep of hot core flow 13 on the pressure side 20. This results in a less mixed fluid stream exiting the flow passages 36.

[0053] By incorporating the leading edge bulge 46 and bowl 48 in an embodiment that includes the flush trough 38, the incoming horseshoe vortices can be displaced with local streamline curvature for the combustion gases 12 around the bulge 46. Similarly, the radially outward migration of the horseshoe vortices can be interrupted early in the flow passage 36 with the bowl 48.

[0054] As previously avoided, the jet trough 38 is effective in changing the local stagnation point at the base of the airfoil, for directing the jet stream into the core flow, which controls the extent of mixing that occurs, as well as controlling the trajectory of the jet stream and its subsequent coalescence with the suction-side leg of the horseshoe vertebra.

[0055] When included, the bulge 46 and bowl 48 are effective in reducing flow acceleration for the combustion gases 12, thereby increasing local static pressure, changing gas pressure gradients, reducing vortex stretching, and reducing reorientation of the horseshoe vortices as they travel downstream through the flow passages 36. These combined effects limit the ability of the horseshoe vortices to migrate radially outward along the airfoil suction side 22, reducing the vortex strength, and in turn increasing the overall efficiency of the turbine stage.

[0056] As indicated above, FIG. 2 is a plan view of the platforms 16 with isoclines for equal elevation in relation to the zero-reference surface. Figure 3 illustrates the platforms 16 in isometric view with superimposed surface gradient lines, to highlight the varying 3D contour of the platforms 16 between the forward and aft ends of each platform 16 and circumferentially or laterally between adjacent airfoils 14.

[0057] Since the platforms 16 extend on both sides of each airfoil 14, typically with small extensions forward of the leading edge 24 and aft of the trailing edge 26, the flush trough 38, the raised bulge 46 and the submerged bowl 48 will transition smoothly into each other in a preferred manner to minimize mixing of the flush stream 15 and reduce the strength of the horseshoe vortices. The bulge 46 is preferably reduced in height or elevation as it extends aft and laterally along the pressure side 20 to join the bowl 48 along the suction side 22, and the flushing trough 38 extends into the mixing area 40 of the platform 16 towards the flushing cavity. The bowl 48 extends along the suction side 22 between the front and rear edges 24, 26, starting, for example, near the front edge 24, and gradually transitions into the flushing trough 38 and ends approximately midway between the airfoil 14 towards the rear edge 26.

[0058] Figures 2-4 best illustrate that the flushing trough 38 is configured laterally off-center with maximum depth at the suction side 22 in front of the front edge 24, to extend into the mixing area 40 of the platform 16. The flushing trough 38 continues gradually into the bowl 48 aft of the leading edge 24.

[0059] Figures 2 and 4 best illustrate that the bulge 46 is centered with maximum height at the pressure side 20 of the airfoil 14, aft of the leading edge 24, and decreases in height aft of the leading edge 24 and towards the trailing edge 26, as well as in lateral direction or circumferential direction from the pressure side 20 of an airfoil 14 towards the suction side 22 of the next nearby airfoil 14.

[0060] Figures 2 and 5 best illustrate that the bowl 48 is centered with maximum depth at the suction side 22 near the maximum lateral thickness of each airfoil in its hump region, and goes aft of the leading edge 24 gradually into the flush trough 38, while it decreases in depth towards the rear edge 26, as well as laterally or in the circumferential direction from the suction side 22 of an airfoil 14 towards the pressure side 20 of the next nearby airfoil 14, where it joins with the raised bulge 46.

[0061] Figure 4 schematically illustrates the incoming combustion gases 12 having a corresponding boundary layer where the velocity of the combustion gases 12 is zero directly at the flow surface of the platform 16, and rapidly increases to the free-flow velocity. The thickness of the boundary layers varies from approximately 2% to approximately 15 percent of the radial height or span of the airfoil 14. In addition, the incoming flush flow 15 is illustrated on the flush trough 38. The size of the platform waveform, including the flush trough 38, and the optional bulge 46 and bowl 48 , may be relatively small to specifically minimize losses due to secondary flows, minimize mixing of the flush flow 15 with the core flow 13, and reduce the strength of the horseshoe vortices to increase the aerodynamic efficiency of the tubine.

[0062] The flushing trough 38, as shown in fig. 2 and 4, has a maximum depth that can be scaled with the level of the flushing current. The bulge 46, as shown in fig. 2 and 4, has a maximum height which is generally equal to the thickness of the incoming boundary layer of combustion gases 12 when they are first channeled over the platforms 16. Correspondingly, the bowl 48 has a maximum depth which is less than an approximately maximum height of the bulge 46. In fig. 2, the isoclines have been labeled with arbitrary numbers from the zero-reference surface, with the bulge 46 increasing in height to an exemplifying magnitude of about +6, with the bowl 48 increasing in depth to a maximum depth of about -5, and the trough 38 gradually passing over in the bowl 48 and on the mixing area 40 of the platform 16 and has a maximum depth of approximately -3.

[0063] These exemplary figures are only representative of the variable contour of the corrugated platform 16. The actual sizes of the trough 38, the bulge 46 and the bowl 48 will be determined for each particular design, with the maximum depth of the trough 38 varying from 0.25 to 1.1 mm, and the bowl varying from about 0.94 mm to about 1.6 mm, and the height of the bulge 46 varying from about 1.0 mm to about 11.4 mm for turbine airfoils varying in height from 5 cm to about 7.5 cm.

[0064] Figures 2 and 4 also illustrate that the flush trough 38 is generally hemispherical tangentially to the flush cavity, and more specifically in the mixing area 40 of the platform 16, and generally concave laterally from its starting point for maximum depth which is positioned directly in and which extends itself over the mixing area 40 of the platform 16 between the forward edge 24 and the suction side 22 of the airfoil 14. The flushing trough 38 extends aft towards the rear edge 26 to gradually transition into or smoothly transform into the bowl 48 when it is present. The bulge 46 is generally hemispherical towards the pressure side 20 of the airfoil 14, and generally convex both forward towards the front edge 24 and in the direction aft towards the rear edge 26. In the axial plane which extends in the circumferential direction between the front edges 24 of the airfoil row, the bulges 46 are conical in section between the convex forward and aft portions thereof in the exemplary embodiment illustrated in fig. 4, for which computational flow analysis predicts a significant reduction in vortex strength and migration. The exemplary bowl 48 illustrated in FIG. 2 and 5 is generally concave laterally from its starting point of maximum depth which is positioned directly on the suction side of each airfoil 14, and which gradually transitions into the flushing trough 38. The bowl 48, like the bulge 46, is generally hemispherical in shape, but concave centered on the suction side of the airfoil 22.

[0065] Figures 2 and 4 illustrate the transition between the flush trough 38 and the bowl 48 on the suction side 22 of the airfoil, and the raised bulge 46 on the pressure side 20 of the airfoil. More specifically, the bulge 46 configured aft of the front edge 24 on the pressure side 20 is gradually reduced, along the longer extension of the pressure side 20 to the rear edge 26. The gradual transition of the bulge 46 to the rear edge 26 forms a dorsal extension of the bulge 46 which is reduced in elevation.

[0066] Correspondingly, the flushing trough 38 and the bowl 48 increase in depth gradually towards the front edge 24 of the airfoil 14 and on the mixing area 40 to form an inlet for the flushing flow 15. The flushing trough 38 and the submerged bowl 48 gradually transition into the raised bulge 46 , gradually along the longer extent of the suction side 22 aft of the rear edge 26, as best illustrated in fig. 2 and 3.

[0067] Figures 2 and 5 illustrate that the flushing trough 38 gradually enters the bowl 48, which decreases in depth along the suction side 22 from its maximum depth extending from the flushing trough 38 near the mixing area 40 of the platform to near the hump of the airfoil towards the rear edge 26. The bulge 46 continuously decreases in height along the pressure side 20 from its maximum height aft of the leading edge 24 to the rear edge 26. Both the bulge 46 and the bowl 48 gradually merge around the rear edge 26 and terminate laterally or circumferentially in the corresponding flow passages 36 between the rear edges 26 at the zero-reference elevation.

[0068] Figures 2 and 4 illustrate that the flush troughs 38, which preferably begin or start in front of the front edges 24 and are transformed into the bowls 48 and the bulges 46, which preferably begin or start aft of the front edges 24, laterally between them form or delimit an axial arcuate gutter or channel 42 along the zero elevation contour therebetween. The trough-shaped channel 42 extends axially along the individual platform 16 between adjacent airfoils 14, beginning in front of the leading edges 24 and terminating at the trailing edges 26, or aft thereof, as desired, within the available surface space of the platforms 16.

[0069] The zero elevation contours may be a single line, or a land of suitable width, between the bulge 16 and the bowl 48. In the land embodiment, the convex bulge 46 preferably gradually transitions into one side of the land through a bend region with a concave transition with the country. The flush trough 38 and the concave bowl 48 preferably gradually merge with the other side of the land through another bending region with a convex transition with the land.

[0070] Since the exemplary turbine stage illustrated in the figures is configured as a turbine rotor stage, the individual platforms 16 are fully joined at the base of each airfoil 14, with a corresponding dovetail 18 (Fig. 2) there below, where the platforms 16 jointly delimits the radially inner boundary or end walls for the stream 12 of combustion gas. Each platform 16 therefore adjoins an adjacent platform at an axial split line 56, the split lines 56 bisecting or splitting the intermediate airfoil bowls 48 axially between the front and rear edges 24, 26 into complementary first bowl portions 52 and second bowl portions 54. is best illustrated in fig. 2, where the platform 16 has parts that extend from the opposite pressure and suction sides 20, 22 of the air foil 14. The bulge 46 is arranged primarily on the pressure side 20 of the platform 16. The suction side part 22 of the platform 16 includes the first bowl part 52 that extends extending over most of the surface of the platform 16 and extending into the mixing area 40 of the flushing cavity to form the flushing trough 38.

[0071] The first bowl part 52 is, however, interrupted by the axial split line 56 from the complementary second bowl part 54 which is formed in one with the bulge 46 on the pressure side 20 of the next nearby platform 16. The first bowl part 52 on a platform 16 is complementary to the second bowl portion 54 on the next adjacent platform 16, jointly delineating a single, complete flush trough 38 with a transition and a bowl 48 extending from the suction side 22 of an airfoil 14 to the bulge 46 and its ridge along the pressure side 20 of the next closest airfoil 14.

[0072] The axial split lines 56 break the circumferential continuity of the entire turbine row stage, and allow individual fabrication of each turbine blade in a conventional manner, such as by casting. The overall configuration of the turbine blade including its airfoil 14, platform 16 and dovetail 18 can be molded in a conventional manner, and its wavy features can also be molded into one therein, where practicable.

[0073] The platforms 16 can alternatively be cast with nominally axisymmetric platforms with locally raised material for the bulge 46, which can then be machined using conventional electrical discharge machining (EDM) or electro chemical machining (ECM) to form 3D - the contour of the wave-shaped platform 16, including the final contours of the flush trough 38, the bulge 46 and the bowl 48.

[0074] Since the gradient lines for the bowl portions 48 on the suction side 22 of the airfoil 14, as illustrated in fig. 2, generally runs in the circumferential direction, the 3D bowl contours can be changed to 2D contours that vary linearly in the circumferential direction to more easily permit molding thereof using conventional mold halves, if desired.

[0075] A significant feature of the wave-shaped platforms 16 illustrated in fig. 2 and 4, the flushing trough 38 is arranged to extend into the mixing area 40 of the flushing cavity, and which extends aft to gradually transition into the bowl 48. Each flushing trough 38 is preferably configured to extend in the lateral direction between the front edges 24 of nearby airfoils 14, and more specifically between the leading edge 24 and the suction side 22 of the airfoil. In an alternative embodiment, the flush troughs 38 may be configured to extend laterally in front of the leading edge 24 of an airfoil, and extend in a lateral position just forward of a diminishing aspect of the bulge 46 of the adjacent airfoil 14 to the suction side 22 of the airfoil (described herein). The flushing troughs 38 quickly transition into the corresponding bowl 48 which extends over the majority of the suction side 22.

[0076] The flush troughs 38 provide a reduction in mixing of the flush flow 15 and the core flow 13, which minimizes a subsequent downsweep of the core flow 13 on the pressure side 20, to backfill with fluid and weaken the formation of horseshoe vortices at their inception. The flush troughs 38 further modify the cross-passage static pressure gradient that provides energy to the horseshoe vortices. The raised bulge 46, configured directly aft of the leading edge 24, provides additional weakening of the horseshoe vortices. Each bulge 46 preferably extends for the greater part from aft of the forward edge 24 and in a direction aft along the pressure side 20 to the rear edge 26.

[0077] The contour of each airfoil 14, and twist or angular position thereof, is selected for each design application, so that the leading edge 24 of the airfoil 14 first receives the combustion gases 12, typically at an oblique angle from the axial centerline axis, and the scavenge stream 15, which keeps it close to the surface of the platform 16 when it is lifted by the platform 16 on the suction side 22. The combustion gases 12, like the core stream 13, and the scavenge stream 15 are rotated as they flow through the curved flow passages 36 between the airfoils 14. The natural stagnation point for the incoming combustion gases 12 can be aligned with the front edge 24 itself, or aligned closely adjacent to it either on the pressure or suction sides 20, 22 of the airfoil 14.

[0078] Accordingly, for each particular design application, at least one of the trough 38 or the bulge 46 may be centered at the natural stagnation point near the leading edge region of the airfoil 14. The thus positioned trough 38, bulge 46 and the complementary bowl 48 is specifically introduced into the radially inner platforms 16 of the turbine rotor blades 10 to cooperate with each other synergistically to reduce the mixing of the jet flow 15 with the core flow 13 and modify the static pressure gradient of the cross passage which drives the horseshoe vortices towards the airfoil suction side 22, which reduces the strength of the horseshoe vortices that are stretched and packed around the leading edge 24 and flow downstream through the flow passages 36.

[0079] The combination of reduced loss due to secondary flows, vortex strength and changed pressure gradients reduces migration of the vortices towards the airfoil suction side 22, and reduces the tendency of the vortices to migrate along the span of the airfoil 14 to correspondingly reduce losses in the turbine's aerodynamic efficiency.

[0080] Another exemplary embodiment is shown in fig. 6 and 7. Each of these figures is similar to that in fig. 1, respectively 2, discussed above. In each of the illustrated figs. 6 and 7, in addition to the flushing trough 38, the bulge 46 and the bowl 48, however, a rear edge ridge 50 is configured at the rear edge 26 of the airfoils 14. In a similar manner to the bulge 46 previously discussed, the rear edge ridge 50 is a bulging or wave-shaped platform which rises upwards (+) into the flow passage 36 from the platforms 16 which delimit the radially inner end walls. It is also taken ad notam that in the illustrated embodiment in fig. 6 and 7, the flush trough 38 is configured with a maximum depth at the leading edge 24, and more specifically at approximately 0% of the width "x" of the passage 36 (previously described) and extends into both the mixing area 41 and at least a part of the flushing cavity wall 41. It should be understood that in an alternative embodiment, a flushing trough 38 is configured as described in fig. 2-6 expected in connection with the described rear edge ridge 50.

[0081] In the embodiment depicted in fig. 6 and 7, the rear edge ridge 50 is shown in a configuration with the flush trough 38, the bulge 46 and the bowl 48. In another embodiment, however, only the flush trough 38 and the rear edge ridge 50 are present. In a further exemplifying embodiment, the rear edge ridge 50 is connected to one of the bulge 46 formation or the bowl 48 formation. The present disclosure is not limited in this regard, as the combination of corrugated surfaces used is selected for certain operational and design parameters, such as mass flow rate, etc.

[0082] Similar to the discussion relating to the bulge 46, the trailing edge ridge 50 rises into the flow passage 36. As shown by the contour lines near the trailing edge 46, in FIG. 7, the slope of the rear edge ridge 50 is steeper than that of the bulge 46. In other exemplary embodiments, however, the slope may be similar to, or less than, that of the bulge 46.

[0083]Furthermore, in an exemplary embodiment, the structure of the rear edge ridge 50 closest to the rear edge 26 has the steepest slope, while as the distance from the rear edge 26, along the platform 16, increases, the slope decreases and becomes more gradual. so that a more gradual and even transition to the platform 16 surface is provided.

[0084] The presence of the rear edge ridge 50 can modify the loading of the airfoil 14 near the end wall. This modification can result in increased lift, a modification of the horseshoe and secondary flow structures, a change in the shock structures and accompanying losses, as well as a modification of the heat transfer.

[0085] By allowing the rear edge ridge 50 to gradually enter the rear edge 26 of the airfoil 14 and the platform 16, an increase in the aerodynamic efficiency of the airfoil 14, and thus the turbine as a whole, can be achieved. Namely, the rear edge ridge 50 can act to increase the area for aerodynamic loading of the airfoil forming the airfoil 14. By increasing the area that can carry load, the operational performance of the turbine can be increased, resulting in more work being extracted from the turbine . Put another way, the inclusion of the trailing edge ridge 50 may, in this embodiment, act to extend the line of curvature of the airfoil 14 near the end wall. Further load beyond the rear edge 26 can thus be carried. The aerodynamic effect of this additional load acts as an over-curvature of the airfoil 14, where the end wall load is reduced near the center passage of the airfoil 14, but is increased near the trailing edge 26. Speeds near the end wall are thus slower, the camber is increased and the primary turbine flow is shifted towards the mid-span section. The result of this effective overcurvature is a reduction in surface friction and secondary current. An overcurvature that is effective is thus achieved in the turbine without modifying the entire airfoil 14.

[0086] Additionally, the presence of the trailing edge ridge 50 allows manipulation of the operational thermal profile at the trailing edge 26 of the airfoil 14. This is because the modification in secondary flow (discussed above) can alter or cause a reduction in convective mixing and/or heat transfer which can normally bring the hot core flow 13 into contact with the end walls. The rear edge 26 of the airfoil 14 can be the location for high temperature concentrations, thus limiting the structural performance of the blade 10 and the end wall at the rear edge 26. The inclusion of the rear edge ridge 40 allows manipulation of the thermal profile. A desired thermal distribution can thus be achieved, and can be optimized, resulting in a reduction in the required cooling.

[0087] The shape and undulating contour of the rear edge ridge 50 together with the flushing trough 38, regardless of whether it is used together with the bulges 46 and/or the bowls 48, is determined to optimize performance of the airfoils 14 and the turbine. For example, the shape of the rear edge ridge 50 is optimized either for aerodynamic performance or durability or both, depending on the desired performance parameters and characteristics.

[0088] As shown in fig. 6 and 7, the rear edge ridge 50 borders directly up to the rear edge 26 of the airfoil 14. Furthermore, in the embodiment shown in these figures, the rear edge ridge 50 borders up to both the suction side 22 and the pressure side 20 of the airfoil. In another embodiment, it borders trailing edge ridge 50 extends up to and extends from trailing edge 26, as shown, and borders up to only one of the printing side

20 or suction side 22, depending on design and operational parameters. In a further alternative embodiment, the trailing edge ridge 50 abuts and extends from the trailing edge 26, as shown, but does not abut either the pressure side 20 or the suction side 22.

[0089] In a further exemplary embodiment, an additional bulge and/or bulge (not shown) may be positioned on the surface 16 at a point downstream of the rear edge ridge 50. In such an embodiment, the bulge and/or bulge may assist in the suppression of vortices or otherwise optimize the operational and performance parameters of various embodiments of the present disclosure.

[0090] In the embodiments shown in fig. 6 and 7 is the maximum height (ie, positive (+) displacement above platform 16) of trailing edge ridge 50 at trailing edge 26, and the height of trailing edge ridge 50 decreases as trailing edge ridge 50 extends away from airfoil 14 surfaces . The rear edge ridge 50 smoothly transitions into the surface 16, to effect effective structural and thermal load distribution. In an embodiment where the flush trough 28, the rear edge ridge 50 and either one, or both, of the bulge 46 and the bowl 48 undulating surfaces are present, the rear edge ridge 50 is smoothly converted to these surfaces and the reference surface as optimized for design and performance purposes.

[0091] In an embodiment where the rear edge ridge 50 and the bulge 46 are included, the maximum height of the rear edge ridge 50 may correspond to that of the bulge 46, which has a maximum height generally equal to the thickness of the incoming boundary layer for combustion gases 12 (see previous discussion). It is conceivable, however, that based on varying operational parameters, the height of the rear edge ridge 50 may be higher than, or lower than, the height of the bulge 46.

[0092] In an exemplary embodiment, as with the trough 38, the bulge 46 and the bowl 48, the rear edge ridge 50 connects the foot end of the airfoil 14 and the rear edge 26 with a rounding type structure suitable to provide the required structural integrity and performance .

[0093] As previously discussed, in one embodiment, the platforms 16 are completely joined to the base of each airfoil 14. Manufacturing an embodiment with a flushing trough 38 and a rear edge ridge 50 as described above may be similar to the manufacturing methods previously discussed. The overall configuration of the turbine blade including its airfoil 14, platform 16 and dovetail 18 can be cast in a conventional manner, and the wave-shaped platform including at least the wash trough 38 and the rear ridge 50 can be cast in one therein, where feasible . Alternatively, the platforms 16 can be cast with nominally axisymmetric platforms with locally raised material for the rear edge ridge 50, which can then be machined using conventional electrical discharge machining (EDM) or electro chemical machining (ECM) to form 3D- the contour of the undulating platform, including the final contours of the ridge. All other known and used methods of production can of course be used, as the various embodiments of the present disclosure are not limited in this respect.

[0094] In an exemplary embodiment, the orientation of the trailing edge ridge 50 is such that it follows the mean line of curvature of the airfoil shape. However, the present embodiment is not limited in this respect, as the orientation and overall shape of the rear edge ridge 50 and its contour must be optimized so that the desired operational and performance parameters are achieved. It is well within the ability of a skilled professional to carry out such optimization.

[0095] The wave-shaped platforms have been disclosed above for a turbine rotor, but can also be applied to a turbine nozzle. In a turbine nozzle, the turbine blades are mounted integrally in radially outer and inner end walls or rings, which are typically axisymmetric circular profiles around the centerline axis. Both the inner and outer rings may be corrugated in a manner similar to that disclosed above, to reduce the negative effects of the corresponding secondary vortices generated at the opposite ends of the turbine nozzle blades and increase aerodynamic loading and efficiency while providing advantageous thermal distribution.

[0096] The wave-shaped platform 16 can therefore be used to increase aerodynamic efficiency in any type of turbine engine, and for any type of turbine airfoil. Further examples include bladed discs (blisks) for turbine rotors, where the airfoils are integrally formed with the perimeter of the rotor disc. Low-pressure turbine blades may include integral outer casings where the wave-shaped platform may also be introduced. Furthermore, steam turbine blades and vanes may also include the wave-shaped platforms at the corresponding foot ends thereof. In addition, various embodiments can be used in other similar applications, such as pumps, fans, turbines and the like. Embodiments disclosed herein are not limited in this respect.

[0097] Modern computer fluid dynamics analysis now allows evaluation of different permutations of the wave-shaped platforms 16 to minimize mixing of a flush flow 15 and a core flow 13, while reducing eddies to increase the turbine's efficiency. The specific contours of the flush troughs 38, bulges 46, bowls 48 and rear ridges 50 will vary as a function of the specific design, but the shape of the flush trough 38 extending into the mixing region 40 of the flush cavity, the raised bulge 46 on the pressure side of the airfoil 20 at the front edge 24, the submerged bowl 48 along the suction side 22 which gradually transitions into the flush trough 38, and the trailing edge ridge 50 at the airfoil trailing edge 26 will remain similar to specifically reduce the negative effects of the mixing of the flush flow 15 with the core flow 13 and effects of vortices generated when the combustion gases 12 split over the front edges 24 of the airfoil, reduced aerodynamic load and undesirable thermal distributions.

[0098] In different embodiments, respectively, the flushing troughs 38, the bulges 46, the bowls 48 and the rear ridges 50 gradually merge into each other and the airfoil 14 via rounding structures as described here. For example, show that the flush trough 38 and the bowl 48 gradually merge into each other, as well as that the flush trough 38 and the bulge 46 gradually merge into each other with roundings, while the rear edge ridge 50 and the bowl 48 gradually merge into each other. It should be understood that the overall contours, gradual transitions and rounding structures can be optimized as necessary.

[0099] Although what are believed to be the preferred and exemplary embodiments of the present disclosure have been described herein, other modifications will be apparent to those skilled in the art from the teachings set forth herein, and are therefore desirable that the appended claims protect all such modifications as fall within the true spirit and scope of the disclosure.

Claims (10)

1. Turbine stage, comprising: a row of airfoils (14) fully joined to corresponding platforms (16) and laterally spaced to define respective flow passages (36) therebetween for channeling gases (13, 19), each flow -passage (36) has a width; each of said airfoils (14) includes a concave pressure side (20) and a laterally opposite convex suction side (22) extending in line between opposite front and rear edges (24, 26); and at least some of said platforms (16) have an undulating flow surface including a flush trough (38) extending tangentially into a mixing area (40) and at least a portion of a flush cavity wall (41) of the platform (16) ), and extends axially towards the suction side (22) of the airfoil (14), aft of the leading edge (22), to channel a flushing flow (19). 2. Turbine stage as set forth in claim 1, wherein said flushing trough (38) is configured with a maximum depth laterally at a location -10% to 60% of the width of the passage (36) formed between the front edges (24) of adjacent airfoils ( 14), where such measurement is measured starting from the front edge (24) of a first airfoil (14) which extends in the lateral direction towards the convex suction side (22) of the first airfoil (14) and towards the front edge (24) of a second nearby airfoil (14) at the concave pressure side (20) of the second nearby airfoil (14). 3. Turbine stage as stated in claim 2, where the flushing trough (38) is configured with a maximum depth location at a position axially downstream of the front edges (24) and inside the passage (36) formed therebetween. 4. Turbine stage as stated in claim 2, where said flushing trough (38) is configured with a maximum depth in the lateral direction at a location approximately midway between the front edges (24) of nearby airfoils (14). 5. Turbine stage as stated in claim 1, where said flushing trough (38) is configured with a maximum depth axially at a location in front of the front edge (24) of the airfoil (14). 6. Turbine stage as stated in claim 1, where at least some of said platforms (16) include a bulge (46) which extends along a portion of said airfoils (14) and is connected to said at least some platforms (16), the bulges (46) border up to said pressure side (20) aft of said front edge (24) of each respective airfoil (14) with the respective platforms (16). 7. Turbine stage as stated in claim 1, where at least some of said platforms (16) include a bowl (48) which extends along a portion of said airfoils (14) and is connected to said at least some platforms (16), the bowls (48) border up to said flushing trough (38) and said suction side (22) aft of said front edge (24) of each respective airfoil (14) with the respective platforms (16). 8. Turbine stage as set forth in claim 1, where at least some of said platforms (16) include a rear edge ridge structure (50) which extends along a portion of said airfoils (14) and is connected to said at least some platforms ( 16), the rear edge ridge structures (50) adjoin said pressure side (20), said suction side (22) and said rear edge (26) of each respective airfoil (14) with the respective platforms (16). 9. Turbine blade (10) comprising: an airfoil (14) fully joined to a platform (16), and with laterally opposed pressure and suction sides (20, 22) extending in line between axially opposite leading and trailing edges (24 , 26); and said platform (16) includes a flushing trough (28) extending tangentially into a mixing area (40) and at least a portion of a flushing cavity wall (41) of the platform (16), the flushing trough (38) extending axially towards the suction side (22) of the airfoil (14), aft of the leading edge (24), to channel a flush flow (19). 10. Blade (10) as stated in claim 9, further including a bulge (46) which borders up to said pressure side (20) aft of said front edge (24), a first bowl part (52) which borders up to said flushing trough (38) ) and said suction side (22) aft of said front edge (24), and a second bowl part (54) formed in one with said bulge (46) on said pressure side (20), and which is complementary to said first bowl part (52), thereby on a nearby blade (10) to delimit a common bowl (48).